Help! - 68gr in 16" middy giving 8 to 10" groups

[joeg26er]

I just got some Hornady 68gr bthp match
is very inaccurate in 1/9 twist 16" middy
talking 8 to 10" groups at 100 yards - not joking

68gr hornady bthp match
26.6gr W748 gives 2850 fps
loaded to max oal to fit GI mag

On the other hand, the rifle is capable of MOA, perhaps even sub MOA
if I do my part even handicapped with a 2MOA red dot
with
55gr Win fmj bt wc
26.6gr W748 gives 2750 fps
loaded to 2.223 inches
Win SR Primers
S&B cases

First question is: how can I load the 68gr so it performs even decently...or as accurate as it should.

Second Question - Am I simply loading the 68gr too long?

PS - the chamber is tight on this AR
by tight I mean when a round is chambered, it is real hard to extract it by pulling on the charging handle. It does extract properly when fired.
yes, I am FL re-sizing with Hornady dies

 

[jpwilly]

Odds are the 68gr is too much for the 1-9 to stabalize...

 

[SquirrelNuts]

68 gr bullet is way too long for 1 in 9 twist. You need something around 55 gr for 1 in 9 twist.

 

[Clarence]

Too much bullet for 1-9" barrel

Nothing else you can say bout that.

 

[unclesam099]

I've had decent success with the 60gr Hornady V-Max loaded to max for the magazine and with 25.3gr of Varget. I shot standing at 100yds and was holding easily on a 15" x 15" piece of white cardboard that I was blasting at. This is a 1:9" twist 16" chrome-lined HBAR, 5.56 chambered, with something like 750rds thru it.

Take a look at the length of the bullet and how much of it will contact the rifling. Some of those heavier bullets will contact the barrel a bit more than others. I believe that you (we) can shoot up to a 69gr bullet, but it's gotta be the right one The Sierra Match King (I believe) is shorter so maybe give that a shot.

 

[ants]

Don't get discouraged. It will improve but you gotta work at it.

There are a half dozen variables in developing any load. That's why load development is a process. You don't just shoot one load, and then cry help. You keep working on it in a very methodical manner until you've got the most that particular bullet and barrel can deliver.

It is true that 1/9 barrels tend to perform better with shorter bullets, but I shoot 75 grain A-Max in generic 1/9 barrels using Varget, and the accuracy isn't 1 MOA but it's decent. In fact, I think that's the 'accuracy load' listed by Lyman in the 48th Edition for a Colt 1/9 twist barrel with heavy bullets. Get the book and verify that.

It is definitely possible to improve your performance but you have to be willing to work for it.

Your OAL is just fine. Don't monkey with that. Shortening it won't improve things.

 

[kelbro]

I shoot 69gr SMKs in several 1:9 barrels without a problem. I never could get the 68gr Hornadys to group. 16" barrel, 22" barrel, or a 24" barrel.

 

[Runningman]

68gr hornady bthp match
26.6gr W748 gives 2850 fps
loaded to max oal to fit GI mag

Where on Earth did you come up with that load? I'm surprised you are not eating primers and hot burning powder in the face. Current Hornady data list 25.8 as max for AR service rifle with 748 and the 68 grain using Winchester commercial cases. Heaver Military cases would be even less powder with decreased volume. You can not expect good results picking a powder charge off the top of your head. Good loads are developed by testing.

68 and 69 match bullets should be loaded to magazine length.

 

[jpwilly]

I would try another bullet too maybe your 1-9 doesn't like the Hornady bullet but I did the same thing and heavy bullets keyholed from my 1-9 rifle.

 

[nicholst55]

Your load is 2.1 grains over the max that Hodgdon, who makes Winchester powders, lists for a 69 grain bullet (they don't list a 68 grain). Your 1-9" twist should stabilize most bullets up to 75-77 grains.

I'd suggest starting around 24.0 grains and carefully working up towards 24.5 grains, Hodgdon's max. If you can't get it to shoot, try a different powder or bullet.

 

[243winxb]

when a round is chambered, it is real hard to extract it by pulling on the charging handle.

This should not be happening. Are you crimping the rounds and bulging the shoulder?

 

[freakshow10mm]

Seems he's over max load and is getting difficult extraction as a result.

Back down your load to a normal load using data from Hodgdon's site.

 

[bfoosh006]

1n9 is fine for 68-69gr bullets, try a different load. 1n9 will be borderline with 75-77gr bullets. Try one of these...http://www.radomski.us/njhp/cart_tech.htm

 

[freakshow10mm]

That's not really accurate. The twist rate doesn't relate to weight, it relates to length. Given a certain diameter, a weight can vary slightly by design. The ogive of the 68gr Hornady bullet is different from the 69gr SMK bullet, thus making the 68gr Hornady bullet longer than the 69gr SMK.

Generally speaking a bullet within a certain weight range can only be a range of lengths. Most say a 69gr bullet is stabilized in a 9 inch twist, when this is misleading because what it should say is a bullet with a length up to and including most 69gr bullets should be stabilized but there are some lighter bullets that will not stabilize in the 9 inch twist and there will be some heavier bullets that are about the same length that will stabilize. But it's easier to say "most bullets up to 69gr" as that will catch most popular bullets in that length range.

A 69gr ULD/VLD bullet is quite a bit longer than a standard 69gr SMK bullet and will not stabilize in the 9 inch twist barrel.

 

[rcmodel]

68 gr bullet is way too long for 1 in 9 twist.

Thats crazy talk there.

1:12 will handle up to 63 grain semi-pointed.
1:9 will handle up to 75 grain BTHP match bullets.
1:7 will handle up to the heaviest .224 bullets made.

Hornady lists that bullet with 25.8 WW-748 max charge.
Seated to 2.250" OAL.
In a 1/9 Colt AR barrel.

The fact that this load doesn't shoot is probably because it is over max, and the bullet may be on the edge of self destructing in flight out of a 1/9 twist.

BTW: Hard extraction of unfired rounds is almost always the result of too much crimp buckling the case shoulder.

rc

 

[Master Blaster]

BTW: Hard extraction of unfired rounds is almost always the result of too much crimp buckling the case shoulder.

Or the bullet contacting the lands of the barrel when its chambered. back off a tiny bit on the OAL and the powder charge and your groups will shrink.

 

[BsChoy]

I shoot 75gr Hornady BTHP in my 1/9 wilson AR without issues...prob a finicky barrel

 

[TooTaxed]

RCMODEL's twist data is correct.

My older SP1 Colt AR-15 had a 1:12 or 1:14 barrel...shot 55-gr beautifully, but keyholed 62-gr ball. Had to get a 1:9 upper to shoot heavier bullets to 75-gr. My new barrel shoots the 55-gr just fine, also.

It appears your load is too hot and you may be seating too long...your bullet should not quite touch the lands when chambered.

There seems to be a general trade-off between velocity and accuracy...more velocity, less accuracy. Load a few small test batches varying one grain, starting with the lowest load in your manual, to check what your rifle "likes".

 

[rcmodel]

SP-1 had 1:12.

The 1:14 was only found on the very first Air Force Armalite AR-15's & first Army Colt Model 601.

The later Colt Model 602, M16-A1, and civilian SP-1 had 1:12.

The M16-A2 went to 1:7.

rc

 

[joeg26er]

no overpressure signs with this load

Hi-
I have loaded up to 27grains of W748 with 55gr Win bullet
no signs of overpressure
no blown primers
velocities are 2850 approx

I will back down to 24 grains on the 68gr bullet and decrease the OAL and report back

thanks

 

[NuJudge]

I have a 20" 1:9" twist barrel that is about as cussed as the barrel spoken of here. It shoots 52gr match bullets beautifully at 200yds using 26.5gr 748 and a CCI primer. It won't group well with anything heavier.

CDD

 

[Sport45]

Hi-
I have loaded up to 27grains of W748 with 55gr Win bullet
no signs of overpressure
no blown primers
velocities are 2850 approx

But note the differences in pressure with the heavier bullet.

Hodgdon shows 26.3gr (max) of 748 under a 55gr bullet developing 39,000 CUP.

24.5 (again max) of 748 under a 69gr bullet developed 51,500 CUP in their testing.

A little over max with the 69gr bullet is a LOT more pressure than a little over max on with the 55gr bullet.

 

[joeg26er]

more research-

I found some of the following advice:

"68 gr. BTHP is using 25 grains of Varget powder in Win. Brass, Fed. SR primers, and a COL of 2.27". It chronographed at an average 2950 fps out of my Savage Model 12FV with a 26" barrel (1 in 9 twist).

6 shots x 68 gr Hornady BTHP w/25.0 gr W748

I have the 68 grain BTHP match data from the Hornady 6th Edition Manual.
Varget 22.7 - 24.9 grains.

The 9" twist will stabilize the 77 grain bullet because of its stubby shape. It was designed for magazine feeding, which is why it is used by the Army Squad Designated Marksmen. It hits harder and also gives them the 600 yard + range that standard ball will not; at least, not from the short M4 barrel."

Sorry I lost the links for credits on this info but I thank those who posted this info...

 

[DBR]

You can also check the actual twist rate of your barrel with a cleaning rod and a tight fitting patch. All 1:9 barrels are not the same.

Reducing the load and getting at least .010 off the rifling may help.

 

[joeg26er]

definitely

I will reduce the load to 25grains W748 and back off on the OAL to 2.27"

will report back hopefully with happy news